1. Field of the Invention
This invention relates to the field of divider/combiners used for amplifying microwave-frequency electromagnetic energy. More specifically, the invention relates to devices for combining an array of three-terminal amplifying devices at the chip level.
2. Description of the Prior Art
The generation of microwave power at relatively large amplitudes has been accomplished in the past by paralleling plural three-terminal amplifier devices (cells) with bond wires. This simple technique works well at lower frequencies, but, at higher frequencies, amplifier device paralleling presents numerous problems that make it undesirable. Each amplifier device will share input power unequally in the absence of any systematic means of controlling the incident power density at the point input power is divided. Such imbalance between devices cause losses due to circulating currents. Transverse propagating modes occur when devices are connected in parallel with non-zero length lines, and such modes can cause push-pull oscillations between devices that can result in catastrophic failure. The shunting effect of paralleled devices causes high matching circuit losses and narrow bandwidth.
These problems and others have recently encouraged the use of lumped-element cell combining circuits at X-band frequencies. The lumped-element technique employs individual low-pass LC matching networks in an effort to solve the problem of unequal input power sharing. However, due to the lack of inherent isolation, the lumped-element technique is only marginally successful, and does not address the other problems associated with three-terminal cell combining.